Hepatitis C virus (HCV) infection is a major health problem that leads to chronic liver disease, such as cirrhosis and hepatocellular carcinoma, in a substantial number of infected individuals, estimated to be 2-15% of the world's population. There are an estimated 4.5 million infected people in the United States alone, according to the U.S. Center for Disease Control. According to the World Health Organization, there are more than 200 million infected individuals worldwide, with at least 3 to 4 million people being infected each year. Once infected, about 20% of people clear the virus, but the rest can harbor HCV the rest of their lives. Ten to twenty percent of chronically infected individuals eventually develop liver-destroying cirrhosis or cancer. The viral disease is transmitted parenterally by contaminated blood and blood products, contaminated needles, or sexually and vertically from infected mothers or carrier mothers to their offspring. Current treatments for HCV infection, which are restricted to immunotherapy with recombinant interferon-α alone or in combination with the nucleoside analog ribavirin, are of limited clinical benefit as resistance develops rapidly. Moreover, there is no established vaccine for HCV. Consequently, there is an urgent need for improved therapeutic agents that effectively combat chronic HCV infection.
The HCV virion is an enveloped positive-strand RNA virus with a single oligoribonucleotide genomic sequence of about 9600 bases which encodes a polyprotein of about 3,010 amino acids. The protein products of the HCV gene consist of the structural proteins C, E1, and E2, and the non-structural proteins NS2, NS3, NS4A and NS4B, and NS5A and NS5B. The nonstructural (NS) proteins are believed to provide the catalytic machinery for viral replication. The NS3 protease releases NS5B, the RNA-dependent RNA polymerase from the polyprotein chain. HCV NS5B polymerase is required for the synthesis of a double-stranded RNA from a single-stranded viral RNA that serves as a template in the replication cycle of HCV. Therefore, NS5B polymerase is considered to be an essential component in the HCV replication complex (K. Ishi, et al., “Expression of Hepatitis C Virus NS5B Protein: Characterization of Its RNA Polymerase Activity and RNA Binding,” Heptology, 29: 1227-1235 (1999); V. Lohmann, et al., “Biochemical and Kinetic Analysis of NS5B RNA-Dependent RNA Polymerase of the Hepatitis C Virus,” Virology, 249: 108-118 (1998)). Inhibition of HCV NS5B polymerase prevents formation of the double-stranded HCV RNA and therefore constitutes an attractive approach to the development of HCV-specific antiviral therapies.
HCV belongs to a much larger family of viruses that share many common features.
Flaviviridae Viruses
The Flaviviridae family of viruses comprises at least three distinct genera: pestiviruses, which cause disease in cattle and pigs; flavivruses, which are the primary cause of diseases such as dengue fever and yellow fever; and hepaciviruses, whose sole member is HCV. The flavivirus genus includes more than 68 members separated into groups on the basis of serological relatedness (Calisher et al., J. Gen. Virol, 1993,70,37-43). Clinical symptoms vary and include fever, encephalitis and hemorrhagic fever (Fields Virology, Editors: Fields, B. N., Knipe, D. M., and Howley, P. M., Lippincott-Raven Publishers, Philadelphia, Pa., 1996, Chapter 31, 931-959). Flaviviruses of global concern that are associated with human disease include the Dengue Hemorrhagic Fever viruses (DHF), yellow fever virus, shock syndrome and Japanese encephalitis virus (Halstead, S. B., Rev. Infect. Dis., 1984, 6, 251-264; Halstead, S. B., Science, 239:476-481, 1988; Monath, T. P., New Eng. J. Med, 1988, 319, 64 1-643).
The pestivirus genus includes bovine viral diarrhea virus (BVDV), classical swine fever virus (CSFV, also called hog cholera virus) and border disease virus (BDV) of sheep (Moennig, V. et al. Adv. Vir. Res. 1992, 41, 53-98). Pestivirus infections of domesticated livestock (cattle, pigs and sheep) cause significant economic losses worldwide. BVDV causes mucosal disease in cattle and is of significant economic importance to the livestock industry (Meyers, G. and Thiel, H. J., Advances in Virus Research, 1996, 47, 53-118; Moennig V., et al, Adv. Vir. Res. 1992, 41, 53-98). Human pestiviruses have not been as extensively characterized as the animal pestiviruses. However, serological surveys indicate considerable pestivirus exposure in humans.
Pestiviruses and hepaciviruses are closely related virus groups within the Flaviviridae family. Other closely related viruses in this family include the GB virus A, GB virus A-like agents, GB virus-B and GB virus-C (also called hepatitis G virus, HGV). The hepacivirus group (hepatitis C virus; HCV) consists of a number of closely related but genotypically distinguishable viruses that infect humans. There are at least 6 HCV genotypes and more than 50 subtypes. Due to the similarities between pestiviruses and hepaciviruses, combined with the poor ability of hepaciviruses to grow efficiently in cell culture, bovine viral diarrhea virus (BVDV) is often used as a surrogate to study the HCV virus.
The genetic organization of pestiviruses and hepaciviruses is very similar. These positive stranded RNA viruses possess a single large open reading frame (ORF) encoding all the viral proteins necessary for virus replication. These proteins are expressed as a polyprotein that is co- and post-translationally processed by both cellular and virus-encoded proteinases to yield the mature viral proteins. The viral proteins responsible for the replication of the viral genome RNA are located within approximately the carboxy-terminal. Two-thirds of the ORF are termed nonstructural (NS) proteins. The genetic organization and polyprotein processing of the nonstructural protein portion of the ORF for pestiviruses and hepaciviruses is very similar. For both the pestiviruses and hepaciviruses, the mature nonstructural (NS) proteins, in sequential order from the amino-terminus of the nonstructural protein coding region to the carboxy-terminus of the ORF, consist of p7, NS2, NS3, NS4A, NS4B, NS5A, and NS5B.
The NS proteins of pestiviruses and hepaciviruses share sequence domains that are characteristic of specific protein functions. For example, the NS3 proteins of viruses in both groups possess amino acid sequence motifs characteristic of serine proteinases and of helicases (Gorbalenya et al. (1988) Nature 333:22; Bazan and Fletterick (1989) Virology 171:637-639; Gorbalenya et al. (1989) Nucleic Acid Res. 17.3889-3897). Similarly, the NS5B proteins of pestiviruses and hepaciviruses have the motifs characteristic of RNA-directed RNA polymerases (Koonin, E. V. and Dolja, V. V. (1993) Crir. Rev. Biochem. Molec. Biol. 28:375-430).
The actual roles and functions of the NS proteins of pestiviruses and hepaciviruses in the lifecycle of the viruses are directly analogous. In both cases, the NS3 serine proteinase is responsible for all proteolytic processing of polyprotein precursors downstream of its position in the ORF (Wiskerchen and Collett (1991) Virology 184:341-350; Bartenschlager et al. (1993) J. Virol. 67:3835-3844; Eckart et al. (1993) Biochem. Biophys. Res. Comm. 192:399-406; Grakoui et al. (1993) J. Virol. 67:2832-2843; Grakoui et al. (1993) Proc. Natl. Acad Sci. USA 90:10583-10587; Ilijikata et al. (1993) J. Virol. 67:4665-4675; Tome et al. (1993) J. Virol. 67:4017-4026). The NS4A protein, in both cases, acts as a cofactor with the NS3 serine protease (Bartenschlager et al. (1994) J. Virol. 68:5045-5055; Failla et al. (1994) J. Virol. 68: 3753-3760; Xu et al. (1997) J Virol. 71:53 12-5322). The NS3 protein of both viruses also functions as a helicase (Kim et al. (1995) Biochem. Biophys. Res. Comm. 215: 160-166; Jin and Peterson (1995) Arch. Biochem. Biophys., 323:47-53; Warrener and Collett (1995) J. Virol. 69:1720-1726). Finally, the NS5B proteins of pestiviruses and hepaciviruses have the predicted RNA-directed RNA polymerases activity (Behrens et al. (1996) EMBO. 15:12-22; Lechmann et al. (1997) J. Virol. 71:8416-8428; Yuan et al. (1997) Biochem. Biophys. Res. Comm. 232:231-235; Hagedorn, PCT WO 97/12033; Zhong et al. (1998) J. Virol. 72.9365-9369).
Treatment of HCV Infection with Interferon
Interferons (IFNs) have been commercially available for the treatment of chronic hepatitis for nearly a decade. IFNs are glycoproteins produced by immune cells in response to viral infection. IFNs inhibit replication of a number of viruses, including HCV, and when used as the sole treatment for hepatitis C infection, IFN can in certain cases suppress serum HCV-RNA to undetectable levels. Additionally, IFN can normalize serum amino transferase levels. Unfortunately, the effect of IFN is temporary and a sustained response occurs in only 8%-9% of patients chronically infected with HCV (Gary L. Davis. Gastroenterology 18:S104-S114, 2000). Most patients, however, have difficulty tolerating interferon treatment, which causes severe flu-like symptoms, weight loss, and lack of energy and stamina.
A number of patents disclose Flaviviridae, including HCV, and treatments using interferon-based therapies. For example, U.S. Pat. No. 5,980,884 to Blatt et al. discloses methods for retreatment of patients afflicted with HCV using consensus interferon. U.S. Pat. No. 5,942,223 to Bazer et al. discloses an anti-HCV therapy using ovine or bovine interferon-tau. U.S. Pat. No. 5,928,636 to Alber et al. discloses the combination therapy of interleukin-12 and interferon alpha for the treatment of infectious diseases including HCV. U.S. Pat. No. 5,849,696 to Chretien et al. discloses the use of thymosins, alone or in combination with interferon, for treating HCV. U.S. Pat. No. 5,830,455 to Valtuena et al. discloses a combination HCV therapy employing interferon and a free radical scavenger. U.S. Pat. No. 5,738,845 to Imakawa discloses the use of human interferon tau proteins for treating HCV. Other interferon-based treatments for HCV are disclosed in U.S. Pat. No. 5,676,942 to Testa et al., U.S. Pat. No. 5,372,808 to Blatt et al., and U.S. Pat. No. 5,849,696. A number of patents also disclose pegylated forms of interferon, such as U.S. Pat. Nos. 5,747,646, 5,792,834 and 5,834,594 to Hoffmann-La Roche; PCT Publication No. WO 99/32139 and WO 99/32140 to Enzon; WO 95/13090 and U.S. Pat. Nos. 5,738,846 and 5,711,944 to Schering; and U.S. Pat. No. 5,908,621 to Glue et al.
Interferon alpha-2a and interferon alpha-2b are currently approved as monotherapy for the treatment of HCV. ROFERON®-A (Roche) is the recombinant form of interferon alpha-2a. PEGASYS® (Roche) is the pegylated (i.e. polyethylene glycol modified) form of interferon alpha-2a. INTRON®A (Schering Corporation) is the recombinant form of Interferon alpha-2b, and PEG-INTRON® (Schering Corporation) is the pegylated form of interferon alpha-2b.
Other forms of interferon alpha, as well as interferon beta, gamma, tau and omega are currently in clinical development for the treatment of HCV. For example, INFERGEN (interferon alphacon-1) by InterMune, OMNIFERON (natural interferon) by Viragen, ALBUFERON by Human Genome Sciences, REBIF (interferon beta-1a) by Ares-Serono, Omega Interferon by BioMedicine, Oral Interferon Alpha by Amarillo Biosciences, and interferon gamma, interferon tau, and interferon gamma-1b by InterMune are in development.
Ribivarin
Ribavirin (1-β-D-ribofuranosyl-1-1,2,4-triazole-3-carboxamide) is a synthetic, non-interferon-inducing, broad spectrum antiviral nucleoside analog sold under the trade name, Virazole (The Merck Index, 11th edition, Editor: Budavari, S., Merck & Co., Inc., Rahway, N.J., p 1304, 1989). U.S. Pat. No. 3,798,209 and RE29,835 disclose and claim ribavirin. Ribavirin is structurally similar to guanosine, and has in vitro activity against several DNA and RNA viruses including Flaviviridae (Gary L. Davis. Gastroenterology 118: 5104-5114, 2000).
Ribavirin reduces serum amino transferase levels to normal in 40% of patients, but it does not lower serum levels of HCV-RNA (Gary L. Davis, 2000). Thus, ribavirin alone is not effective in reducing viral RNA levels. Additionally, ribavirin has significant toxicity and is known to induce anemia. Ribavirin is not approved for monotherapy against HCV. It has been approved in combination with interferon alpha-2a or interferon alpha-2b for the treatment of HCV.
Ribavirin is a known inosine monophosphate dehydrogenease inhibitor that does not have specific anti-HCV activity in the HCV replicon system (Stuyver et al. Journal of Virology, 2003, 77, 10689-10694).
Combination of Interferon and Ribavirin
The current standard of care for chronic hepatitis C is combination therapy with an alpha interferon and ribavirin. The combination of interferon and ribavirin for the treatment of HCV infection has been reported to be effective in the treatment of interferon naïve patients (Battaglia, A. M. et al., Ann. Pharmacother. 34:487-494, 2000), as well as for treatment of patients when histological disease is present (Berenguer, M. et al. Antivir. Ther. 3(Suppl. 3):125-136, 1998). Studies have shown that more patients with hepatitis C respond to pegylated interferon-alpha/ribavirin combination therapy than to combination therapy with unpegylated interferon alpha. However, as with monotherapy, significant side effects develop during combination therapy, including hemolysis, flu-like symptoms, anemia, and fatigue. (Gary L. Davis, 2000). Combination therapy with PEG-INTRON® (peginterferon alpha-2b) and REBETOL® (Ribavirin, USP) capsules are available from Schering Corporation. REBETOL® (Schering Corporation) has also been approved in combination with INTRON® A (Interferon alpha-2b, recombinant, Schering Corporation). Roche's PEGASYS® (pegylated interferon alpha-2a) and COPEGUS® (ribavirin), as well as Three River Pharmacetical's Ribosphere® are also approved for the treatment of HCV.
PCT Publication Nos. WO 99/59621, WO 00/37110, WO 01/81359, WO 02/32414 and WO 03/02446 1 by Schering Corporation disclose the use of pegylated interferon alpha and ribavirin combination therapy for the treatment of HCV. PCT Publication Nos. WO 99/15 194, WO 99/64016, and WO 00/24355 by Hoffmann-La Roche Inc. also disclose the use of pegylated interferon alpha and ribavirin combination therapy for the treatment of HCV.
Additional Methods to Treat Flaviviridae Infections
The development of new antiviral agents for Flaviviridae infections, especially hepatitis C, is currently underway. Specific inhibitors of HCV-derived enzymes such as protease, helicase, and polymerase inhibitors are being developed. Drugs that inhibit other steps in HCV replication are also in development, for example, drugs that block production of HCV antigens from the RNA (IRES inhibitors), drugs that prevent the normal processing of HCV proteins (inhibitors of glycosylation), drugs that block entry of HCV into cells (by blocking its receptor) and nonspecific cytoprotective agents that block cell injury caused by the virus infection. Further, molecular approaches are also being developed to treat hepatitis C, for example, ribozymes, which are enzymes that break down specific viral RNA molecules, antisense oligonucleotides, which are small complementary segments of DNA that bind to viral RNA and inhibit viral replication, and RNA interference techniques are under investigation (Bymock et al. Antiviral Chemistry & Chemotherapy, 11:2; 79-95 (2000); De Francesco et al. in Antiviral Research, 58: 1-16 (2003); and Kronke et al., J. Virol., 78:3436-3446 (2004).
Bovine viral diarrhea virus (BVDV) is a pestivirus belonging to the family Flaviviridae and has been used as a surrogate for in vitro testing of potential antiviral agents. While activity against BVDV may suggest activity against other flaviviruses, often a compound can be inactive against BVDV and active against another flavivirus. Sommadossi and La Colla have revealed (“Methods and compositions for treating flaviviruses and pestiviruses”, PCT WO 01/92282) that ribonucleosides containing a methyl group at the 2′ “up” position have activity against BVDV. However, it is unclear whether these compounds can inhibit other flaviviruses, including HCV in cell culture or at the HCV NS5B level. Interestingly while this publication discloses a large number of compounds that are 2′-methyl-2′-X-ribonucleosides, where X is a halogen, fluorine is not considered. Furthermore, a synthetic pathway leading to nucleosides halogenated at the 2′ “down” position is not shown by these inventors.
Dengue virus (DENV) is the causative agent of Dengue hemorrhagic fever (DHF). According to the world Health Organization (WHO), two fifths of the world population are now at risk for infection with this virus. An estimated 500,000 cases of DHF require hospitalization each year with a mortality rate of 5% in children.
West Nile virus (WNV), a flavivirus previously known to exist only in intertropical regions, has emerged in recent years in temperate areas of Europe and North America, presenting a threat to public health. The most serious manifestation of WNV infection is fatal encephalitis in humans. Outbreaks in New York City and sporadic occurrences in the Southern United States have been reported since 1999.
There is currently no preventive treatment of HCV, Dengue virus (DENV) or West Nile virus infection. Currently approved therapies, which exist only against HCV, are limited. Examples of antiviral agents that have been identified as active against the hepatitis C flavivirus include:    1) Protease inhibitors:
Substrate-based NS3 protease inhibitors (Attwood et al., PCT WO 98/22496, 1998; Attwood et al., Antiviral Chemistry and Chemotherapy 1999, 10, 259-273; Attwood et al., Preparation and use of amino acid derivatives as anti-viral agents, German Patent Pub. DE 19914474; Tung et al. Inhibitors of serine proteases, particularly hepatitis C virus NS3 protease, PCT WO 98/17679), including alphaketoamides and hydrazinoureas, and inhibitors that terminate in an electrophile such as a boronic acid or phosphonate (Llinas-Brunet et al, Hepatitis C inhibitor peptide analogues, PCT WO 99/07734) are being investigated.
Non-substrate-based NS3 protease inhibitors such as 2,4,6-trihydroxy-3-nitro-benzamide derivatives (Sudo K. et al., Biochemical and Biophysical Research Communications, 1997, 238, 643-647; Sudo K. et al. Antiviral Chemistry and Chemotherapy, 1998, 9, 186), including RD3-4082 and RD3-4078, the former substituted on the amide with a 14 carbon chain and the latter processing a para-phenoxyphenyl group are also being investigated.
SCH 68631, a phenanthrenequinone, is an HCV protease inhibitor (Chu M. et al., Tetrahedron Letters 3 7:7229-7232, 1996). In another example by the same authors, SCH 351633, isolated from the fungus Penicillium griseofulvum, was identified as a protease inhibitor (Chu M. et al., Bioorganic and Medicinal Chemistry Letters 9:1949-1952). Nanomolar potency against the HCV NS3 protease enzyme has been achieved by the design of selective inhibitors based on the macromolecule eglin c. Eglin c, isolated from leech, is a potent inhibitor of several serine proteases such as S. griseus proteases A and B, α-chymotrypsin, chymase and subtilisin (Qasim M. A. et al., Biochemistry 36:1598-1607, 1997).
Several U.S. patents disclose protease inhibitors for the treatment of HCV. For example, U.S. Pat. No. 6,004,933 to Spruce et al. discloses a class of cysteine protease inhibitors for inhibiting HCV endopeptidase 2. U.S. Pat. No. 5,990,276 to Zhang et al. discloses synthetic inhibitors of hepatitis C virus NS3 protease. The inhibitor is a subsequence of a substrate of the NS3 protease or a substrate of the NS4A cofactor. The use of restriction enzymes to treat HCV is disclosed in U.S. Pat. No. 5,538,865 to Reyes et al. Peptides as NS3 serine protease inhibitors of HCV are disclosed in WO 02/008251 to Corvas International, Inc. and WO 02/08187 and WO 02/008256 to Schering Corporation. HCV inhibitor tripeptides are disclosed in U.S. Pat. Nos. 6,534,523, 6,410,531, and 6,420,380 to Boehringer Ingelheim and WO 02/060926 to Bristol Myers Squibb. Diaryl peptides as NS3 serine protease inhibitors of HCV are disclosed in WO 02/48172 to Schering Corporation. Imidazoleidinones as NS3 serine protease inhibitors of HCV are disclosed in WO 02/08198 to Schering Corporation and WO 02/48157 to Bristol Myers Squibb. WO 98/17679 to Vertex Pharmaceuticals and WO 02/48116 to Bristol Myers Squibb also disclose HCV protease inhibitors.    2) Thiazolidine derivatives which show relevant inhibition in a reverse-phase HPLC assay with an NS3/4A fusion protein and NS5A/5B substrate (Sudo K. et al., Antiviral Research, 1996, 32, 9-18), especially compound RD-1-6250, possessing a fused cinnamoyl moiety substituted with a long alkyl chain, RD4 6205 and RD4 6193;    3) Thiazolidines and benzanilides identified in Kakiuchi N. et al. J. EBS Letters 421, 217-220; Takeshita N. et al. Analytical Biochemistry, 1997, 247,242-246;    4) A phenanthrenequinone possessing activity against protease in a SDS-PAGE and autoradiography assay isolated from the fermentation culture broth of Streptomyces sp., Sch 68631 (Chu M. et al., Tetrahedron Letters, 1996, 37, 7229-7232), and Sch 351633, isolated from the fungus Penicillium griseofulvum, which demonstrates activity in a scintillation proximity assay (Chu M. et al., Bioorganic and Medicinal Chemistry Letters 9, 1949-1952);    5) Helicase inhibitors (Diana G. D. et al., Compounds, compositions and methods for treatment of hepatitis C, U.S. Pat. No. 5,633,358; Diana G. D. et al., Piperidine derivatives, pharmaceutical compositions thereof and their use in the treatment of hepatitis C, PCT WO 97/36554);    6) Nucleotide polymerase inhibitors and gliotoxin (Ferrari R. et al. Journal of Virology, 1999, 73, 1649-1654), and the natural product cerulenin (Lohmann V. et al, Virology, 1998, 249, 108-118);    7) Antisense phosphorothioate oligodeoxynucleotides (S-ODN) complementary to sequence stretches in the 5′ non-coding region (NCR) of the virus (Alt M. et al., Hepatology, 1995, 22, 707-717), or nucleotides 326-348 comprising the 3′ end of the NCR and nucleotides 371-388 located in the core coding region of the HCV RNA (Alt M. et al., Archives of Virology, 1997, 142, 589-599; Galderisi U. et al., Journal of Cellular Physiology, 1999, 181, 251-257);    8) Inhibitors of IRES-dependent translation (Ikeda N. et al., Agent for the prevention and treatment of hepatitis C, Japanese Patent Pub. JP-8268890; Kai Y. et al. Prevention and treatment of viral diseases, Japanese Patent Pub. JP-101 01591);    9) Ribozymes, such as nuclease-resistant ribozymes (Maccjak, D. J. et al., Hepatology 1999, 30, abstract 995) and those disclosed in U.S. Pat. No. 6,043,077 to Barber et al., and U.S. Pat. Nos. 5,869,253 and 5,610,054 to Draper et al.;    10) Nucleoside analogs have also been developed for the treatment of Flaviviridae infections.
Idenix Pharmaceuticals discloses the use of certain branched nucleosides in the treatment of flaviviruses (including HCV) and pestiviruses in International Publication Nos. WO 01/90121 and WO 01/92282. Specifically, a method for the treatment of hepatitis C virus infection (and flaviviruses and pestiviruses) in humans and other host animals is disclosed in the Idenix publications that includes administering an effective amount of a biologically active 1′, 2′, 3′ or 4′-branched β-D or β-L nucleosides or a pharmaceutically acceptable salt or derivative thereof, administered either alone or in combination with another antiviral agent, optionally in a pharmaceutically acceptable carrier.
WO 2004/002422 to Idenix published Jan. 8, 2004 discloses a family of 2′-methyl nucleosides for the treatment of flavivirus infections. WO 2004/002999 to Idenix, published Jan. 8, 2004 discloses a series of 2′ or 3′ prodrugs of 1′, 2′, 3′, or 4′ branch nucleosides for the treatment of flavivirus infections including HCV infections.
Other patent applications disclosing the use of certain nucleoside analogs to treat hepatitis C virus infection include: PCT/CAOO/01316 (WO 01/32153; filed Nov. 3, 2000) and PCT/CAOI/00197 (WO 01/60315; filed Feb. 19, 2001) filed by BioChem Pharma, Inc. (now Shire Biochem, Inc.); PCTJUSO2/01531 (WO 02/057425; filed Jan. 18, 2002) and PCT/U502/03086 (WO 02/057287; filed Jan. 18, 2002) filed by Merck & Co., Inc., PCT/EPOT/09633 (WO 02/18404; published Aug. 21, 2001) filed by Roche, and PCT Publication Nos. WO 01/79246 (filed Apr. 13, 2001), WO 02/32920 (filed Oct. 18, 2001) and WO 02/48 165 by Pharmasset, Ltd.
WO 2004/007512 to Merck & Co. discloses a number of nucleoside compounds disclosed as inhibitors of RNA-dependent RNA viral polymerase. The nucleosides disclosed in this publication are primarily 2′-methyl-2′-hydroxy substituted nucleosides. WO 02/057287 to Merck et al. published Jul. 25, 2002, discloses a large genus of pyrimidine derivative nucleosides of the 2′-methyl-2′-hydroxy substitutions. WO 2004/009020 to Merck et al. discloses a series of thionucleoside derivatives as inhibitors of RNA dependent RNA viral prolymerase. WO 03/105770 to Merck et al. discloses a series of carbocyclic nucleoside derivatives that are useful for the treatement of HCV infections.
PCT Publication No. WO 99/43691 to Emory University, entitled “2′-Fluoronucleosides” discloses the use of certain 2′-fluoronucleosides to treat HCV. U.S. Pat. No. 6,348,587 to Emory University entitled “2′-fluoronucleosides” discloses a family of 2′-fluoronucleosides useful for the treatment of hepatitis B, HCV, HUV and abnormal cellular proliferation. The 2′ subsitutent is disclosed to be in either the “up” or “down” position.
Eldrup et al. (Oral Session V, Hepatitis C Virus, Flaviviridae; 16th International Conference on Antiviral Research (Apr. 27, 2003, Savannah, Ga.)) described the structure activity relationship of 2′-modified nucleosides for inhibition of HCV.
Bhat et al. (Oral Session V, Hepatitis C Virus, Flaviviridae; 16th International Conference on Antiviral Research (Apr. 27, 2003, Savannah, Ga.); p A75) describe the synthesis and pharmacokinetic properties of nucleoside analogues as possible inhibitors of HCV RNA replication. The authors report that 2′-modified nucleosides demonstrate potent inhibitory activity in cell-based replicon assays.
Olsen et al. (Oral Session V, Hepatitis C Virus, Flaviviridae; 16th International Conference on Antiviral Research (Apr. 27, 2003, Savannah, Ga.) p A76) also described the effects of the 2′-modified nucleosides on HCV RNA replication.    11) Other miscellaneous compounds including 1-amino-alkylcyclohexanes (U.S. Pat. No. 6,034,134 to Gold et al.), alkyl lipids (U.S. Pat. No. 5,922,757 to Chojkier et al.), vitamin E and other antioxidants (U.S. Pat. No. 5,922,757 to Chojkier et al.), squalene, amantadine, bile acids (U.S. Pat. No. 5,846,964 to Ozeki et al.), N-(phosphonoacetyl)-L-aspartic acid, (U.S. Pat. No. 5,830,905 to Diana et al.), benzenedicarboxamides (U.S. Pat. No. 5,633,388 to Diana et al.), polyadenylic acid derivatives (U.S. Pat. No. 5,496,546 to Wang et al.), 2,3-dideoxyinosine (U.S. Pat. No. 5,026,687 to Yarchoan et al.), benzimidazoles (U.S. Pat. No. 5,891,874 to Colacino et al.), plant extracts (U.S. Pat. No. 5,837,257 to Tsai et al., U.S. Pat. No. 5,725,859 to Omer et al., and U.S. Pat. No. 6,056,961), and piperidenes (U.S. Pat. No. 5,830,905 to Diana et al.).    12) Other compounds currently in preclinical or clinical development for treatment of hepatitis C virus infection include: Interleukin-10 by Schering-Plough, IP-SO1 by Intemeuron, Merimebodib (VX-497) by Vertex, AMANTADINE® (Symmetrel) by Endo Labs Solvay, HEPTAZYME® by RPI, IDN-6556 by Idun Pharma., XTL-002 by XTL., HCV/MFS9 by Chiron, CIVACIR® (hepatitis C Immune Globulin) by NABI, LEVOVIRIN® by ICN/Ribapharm, VIRAMIDINE® by ICN/Ribapharm, ZADAXIN® (thymosin alpha-1) by SciClone, thymosin plus pegylated interferon by Sci Clone, CEPLENE® (histamine dihydrochloride) by Maxim, VX 950/LY 570310 by Vertex/Eli Lilly, ISIS 14803 by Isis Pharmaceutical/Elan, IDN-6556 by Idun Pharmaceuticals, Inc., JTK 003 by AKROS Pharma, BILN-2061 by Boehringer Ingelheim, CellCept (mycophenolate mofetil) by Roche, T67, a β-tubulin inhibitor, by Tularik, a therapeutic vaccine directed to E2 by Innogenetics, FK788 by Fujisawa Healthcare, Inc., 1 dB 1016 (Siliphos, oral silybin-phosphatdylcholine phytosome), RNA replication inhibitors (VP50406) by ViroPharma/Wyeth, therapeutic vaccine by Intercell, therapeutic vaccine by Epimmune/Genencor, IRES inhibitor by Anadys, ANA 245 and ANA 246 by Anadys, immunotherapy (Therapore) by Avant, protease inhibitor by Corvas/SChering, helicase inhibitor by Vertex, fusion inhibitor by Trimeris, T cell therapy by CellExSys, polymerase inhibitor by Biocryst, targeted RNA chemistry by PTC Therapeutics, Dication by Immtech, Int., protease inhibitor by Agouron, protease inhibitor by Chiron/Medivir, antisense therapy by AVI BioPharma, antisense therapy by Hybridon, hemopurifier by Aethlon Medical, therapeutic vaccine by Merix, protease inhibitor by Bristol-Myers Squibb/Axys, Chron-VacC, a therapeutic vaccine, by Tripep, UT 231 B by United Therapeutics, protease, helicase and polymerase inhibitors by Genelabs Technologies, IRES inhibitors by Immusol, R803 by Rigel Pharmaceuticals, INFERGEN® (interferon alphacon-1) by InterMune, OMNIFERON® (natural interferon) by Viragen, ALBUFERON® by Human Genome Sciences, REBIF® (interferon beta-la) by Ares-Serono, Omega Interferon by BioMedicine, Oral Interferon Alpha by Amarillo Biosciences, interferon gamma, interferon tau, and Interferon gamma-1b by InterMune. Rigel Pharmaceuticals is developing a non-nucleoside HCV polymerase inhibitor, R803, that shows promise as being synergistic with IFN and ribavirin.    13) A summary of several investigational drugs, including several discussed above, that are currently in various phases of development for the treatment of HCV, are summarized below:
DrugMechanism/TargetCompanyU.S. StatusBILN-2061NS3 Serine-proteaseBoehringer IngelheimPhase IIinhibitorISIS 14803Antisense/PreventISIS/ElanPhase IITranslation of RNAViramidineProdrug of RibavirinRibapharmPhase IINM 283Inhibitor of HCV RNAIdenixPhase II/IIIPolymeraseVX-497IMPDH InhibitorVertexPhase I/IIJKT-003Inhibitor of HCV RNAJapan Tobacco/AkrosPhase I/IIPolymeraseLevovirinL-Ribavirin analogRibapharm/RochePhase I/IIIsatoribine; ANA245Nucleoside analogAnadysPhase IInteract with TLR7receptorAlbuferonImmune modulatorHuman GenomePhase ISciencesPeg-InfergenImmune modulatorIntermunePhase IVX-950Inhibitor of HCVVertexPreclinicalNS3-4A proteaseSCH 6Inhibitor of HCVSchering PloughPreclinicalNS3-4A proteaseR803Inhibitor of HCV RNARigelPhase IpolymeraseHCV-086—ViroPharma/WyethPhase IR1479Inhibitor of HCV RNARochePhase Ipolymerase
Nucleoside prodrugs have been previously described for the treatment of other forms of hepatitis. WO 00/09531 and WO 01/96353 to Idenix Pharmaceuticals, discloses 2′-deoxy-β-L-nucleosides and their 3′-prodrugs for the treatment of HBV. U.S. Pat. No. 4,957,924 to Beauchamp discloses various therapeutic esters of acyclovir.
In light of the fact that HCV infection has reached epidemic levels worldwide, and has tragic effects on the infected patient, there remains a strong need to provide new effective pharmaceutical agents to treat hepatitis C that have low toxicity to the host.
Further, given the rising threat of other flaviviridae infections, there remains a strong need to provide new effective pharmaceutical agents that have low toxicity to the host.